1. Field of the Invention
The present invention relates to the field of computer networking. Specifically, the present invention relates to a method and apparatus for sensing the data transmission speed of a token ring local area network (LAN) when inserting a network device into the token ring LAN, and automatically setting the data transmission speed of the network device accordingly.
2. Description of the Related Art
Token ring local area networks (LANs) are well-known in the art and are described in, for example, the IEEE standard 802.5. IEEE 802.5 token ring LANs adhere to the ISO/IEC 8802-5.2 token ring access method and physical layer specifications. Generally, token ring LANs provide for transmission of a token from node to node in a network. When a node, such as station or a concentrator, is in possession of the token, it may transmit messages, in the form of data packets, onto the communication media. A basic advantage of this networking scheme is that access to the communications media is deterministic and, therefore, collisions that normally occur when two devices transmit at the same time are avoided.
FIG. 1 illustrates a simple token ring LAN 100 having stations 110 and 120 connected thereto. Additionally, token ring LAN 100 has a concentrator 130 connected thereto. Concentrator 130 is further connected to token ring LAN 140, to which stations 150 and 160 are connected. Concentrator 130 provides for communication of a plurality of stations on token ring LAN 100 with a plurality of stations on token ring LAN 140. In other words, while concentrator 130 may source its own data packets on to token ring LANs 100 and 140, its primary purpose is to forward data packets sourced, i.e., transmitted by, a source station on one of token ring LANs 100 and 140 to a destination station on the other token ring LAN.
Token ring LANs generally provide for transmission of data at 4 megabits per second (Mb/s) or 16 Mb/s. In the prior art, when a station was inserted in to a token ring LAN, the data transmission speed of the token ring LAN had to be known and the station manually configured accordingly, so that it would send and receives data packets at the appropriate speed to/from the token ring LAN. Moreover, in the prior art, if the station was configured to send and receive data packets at an incorrect rate, not only would the station be unable to communicate with other stations on the token ring LAN, but the entire token ring LAN would be rendered inoperative.
Also in the prior art, when a concentrator or the like was inserted in to a token ring LAN, the data transmission speed of the token ring LAN to which the concentrator was being connected had to be known so that the port on the concentrator could be configured for the proper data transmission speed. Of course, the concentrator could be coupled to one or more additional token ring LAN via other ports. It was possible that another token ring LANs operated at a different data transmission speed. If fact, one reason for using a concentrator or the like in a token ring LAN environment was to provide for communication between stations connected to token ring LANs operating at different data transmission rates. Thus, each port on the concentrator had to be manually configured to match the speed of the token ring LAN coupled thereto. As was the case with a station, improperly setting the data transmission rate for a port on the concentrator resulted in breaking the token ring LAN so that none of the nodes attached to that token ring LAN could communicate.
Advances have been made in the prior art such that when a node is inserted in to a token ring LAN at the incorrect speed, only the node is unable to communicate with other nodes on the token ring LAN--other nodes, either stations or concentrators, are still able to communicate successfully, assuming they are configured properly, including their data transmission speed setting. Of course, if a port on a concentrator is set to the incorrect speed, it will be unable to forward data packets to or from the token ring LAN attached thereto.
As can be seen by the above discussion of the prior art, a network manager must know the data transmission speed of the token ring LAN to which he or she is coupling a node in order to ensure the node and the token ring LAN are able to operate properly. However, because the node and the token ring LAN can operate and either 4 Mb/s or 16 Mb/s, the installation of a node, including configuration of the appropriate data transmission speed, is susceptible to human error. Thus, what is needed is a method and apparatus for ensuring that a station or concentrator inserted in to a token ring LAN is automatically configured to operate at a data transmission speed that is compatible with the data transmission speed of the token ring LAN.